For a normal story ending, I would give this about a 3 on a scale of 0 to 10. But this is a manga ending, so it is graded on a curve.
About half of manga endings are bad. They are rushed, pair up the wrong two people, or are just thoroughly awful.
Another third of endings are like this one. They author either just stops and says "Fin", or they leave the primary story question unanswered.
And only about one-sixth of manga endings are actually good. Mind you "good" ranges from "merely technically competent" to "perfectly fulfilling", so there is a lot of quality variation in that final sixth.
So that in mind, what score to give this on the manga scale? As it wasn't bad, it was better than half the endings so it is at minimum a 5. And it wasn't good, so it cannot rank in the top sixth, which gives it a maximum of 8.66. That means the midpoint of a non-ending ending is about 6.833. So was there anything to differentiate this non-ending from other non-endings? Yes, instead of just leaving it as a question that will *never* be ended, the manga at least admits that this non-choice cannot be allowed to stand, and aims for a resolution...though the readers can only imagine what it might be. Though this is not satisfying, it is ever so slightly less unsatisfying, which allows us to round this ending's rating up to a flat 7.
So not a good ending, but not so not-good that I hate the entire manga restroactively.